Not criticizing the core idea, which is sound (don't waste ressource overengineering at the beginning, evolve your architecture to match your actual scale as you grow), but the “number of users” figures in this post are completely nonsensical. You ought to multiply them by 100 (if you're being conservative) or even 1000 (depending on the consumption pattern for the user).
Modern hardware is fast, if you cannot fit more than 100 users (not even 100 concurrent users) on a single $50/month server, you're doing something very very wrong.
Even repurposed 10 years old fairphone[1] can handle more than that.
Modern hardware is fast, if you cannot fit more than 100 users (not even 100 concurrent users) on a single $50/month server, you're doing something very very wrong.
Even repurposed 10 years old fairphone[1] can handle more than that.
[1]: https://far.computer